China's securities market regulator and police are cracking down on suspected violations of stock dealing rules and the fabrication of trading information, the latest step in a slew of measures to clean up markets amid wild exchange gyrations.

Police are investigating eight employees of the country's largest brokerage, CITIC Securities Co Ltd, for suspected illegal securities trading, the official Xinhua news agency said.

In a statement to the Hong Kong stock exchange, CITIC Securities said it had not been informed of a probe into staff and the business was operating normally.

An employee and a former employee of the China Securities Regulatory Commission (CSRC) are suspected of insider trading and forging official documents and seals, the agency said.

Wang Xiaolu, a reporter at respected business magazine Caijing is suspected, along with others, of fabricating and spreading false securities and futures trading information, the agency said.

Police summoned Wang, Caijing said in a statement, but it was not given a reason for his detention. It would support actions taken by Wang within the normal course of business, it added.

Caijing said it believed objective reporting promotes the healthy development of the securities market.

In separate stock exchange statements, four Chinese brokerages said the regulator was investigating them for failure to properly identify clients.

Haitong Securities Co Ltd, Founder Securities Co Ltd, Huatai Securities Co Ltd and GF Securities Co Ltd said the CSRC was looking for failures to review and verify client identity, in line with rules.

In July, the CSRC said it would investigate suspected market manipulation after Chinese stock market turmoil started around mid-June.